Abstract Children reared in poverty and those diagnosed with language impairments both perform poorly on standardized measures of language. Yet, the cause of poor performance for the groups is considered quite different, limited experiences and/or test bias as compared to faulty language systems. Further complicating the research is the fact that children from low-income backgrounds often speak a nonmainstream dialect. The goal of the current work is to address these issues by differentiating the language profiles of children from low- income backgrounds and those diagnosed with Specific Language Impairment (SLI) in narrowly defined groups. To accomplish this, we will evaluate past tense marking in four groups of African American English (AAE)-speaking children: 6-year old children from low-income backgrounds, their typically developing age- matched peers from middle income backgrounds, their typically developing language-matched peers from middle income backgrounds, and their typically developing age-matched peers diagnosed with SLI. The children's language abilities will be evaluated using spontaneous language sampling and established protocols for past tense and passive marking. Comparing group performance on these grammatical measures will further test whether the two groups demonstrate general language difficulties or more specific language difficulties (e.g., grammar or vocabulary). Such outcomes will contribute to advances in understanding individual variation across language profiles, further enhancing our diagnostic accuracy of SLI.